Inkjet printers are well known and extremely popular. Particular inkjet printers are described, for example, in U.S. Pat. Nos. 5,648,806, 4,855,752, and 4,967,203. An inkjet printer ejects fine droplets of ink onto a print medium, principally paper, from precisely formed nozzles in one or more printheads. High quality color inkjet printers include printheads, alternatively termed pens, typically for the three subtractive primary color inks, cyan, magenta, and yellow, and a separate printhead for black ink. When printing a color image, droplets, or dots, of the three primary colors are printed in various combinations to achieve the desired color tones, or hues, to reproduce the original color image. Inkjet printers including printheads for additional color inks, for example, for seven color inks, are also known. Multiple drops of the same color may be used for a single color spot to increase the intensity of that color in the color spot.
In an inkjet printer, printing is performed as a print carriage conveying the pens is scanned across a print medium. Printing multiple drops requires multiple passes of the print carriage across the same portion of the print medium. Printing may be performed in both directions, that is as the print carriage sweeps from left to right across the medium and as it sweeps from right to left. The data to be printed on a page is typically partitioned into regions based on the nature of the content of each region. A distinct printmode, or collection of printing techniques, is used to optimize the print quality and printing speed of each region. For example, different printmodes are used for text and for graphics. Printmode parameters include, but are not limited to, the number of drops per location, which is related to the number of passes, output resolution, sweep speed, and sweep direction.
A region is printed during one or more sweeps of the carriage over the medium, and each region is completed before the next is begun. Data from two regions is never printed during the same sweep. Because the height of a given region is almost never an integral multiple of the height of a pen, a portion of the pen extends beyond the region being printed during one or more passes. The nozzles in the portion of the pen that extend beyond the current region go unused. By not using all the available nozzles at any given time, more sweeps are required to print a page than would otherwise be needed if all nozzles were utilized. The time required to print a page is directly proportional to the number of sweeps of the print carriage.
One approach to avoiding carriage sweeps with unused nozzles because of printing adjacent regions with different printmodes, is to print multiple regions with a single, "least common denominator" printmode. This approach avoids the overhead of switching between printmodes, but may result in loss of print quality when the single printmode is not optimal for some of the regions being printed. What is needed is a way to reduce the time to print a page by minimizing unused nozzles while retaining optimal print quality.